With respect to the integration of a Light Emitting Diode (LED) die in an lighting application several levels of packaging/integration may be distinguished. Level 0 is the LED die itself. A LED die is, for example, not suitable for being soldered directly to a printed circuit board and must be integrated into a package and must be equipped with, for example, wire bonds. A level 1 integration is a first level of packaging of the LED die such that the LED die cannot be touched anymore by a person and such that the LED die can be connected to other circuitries. In the level 1 package the LED die is, often, connected with wire bonds to external contacts of the level 1 package. A subsequent level of integration level is providing the Level 1 LED package to, for example, a printed circuit board.
Today several lighting application comprise Level 1 LED packages in which several LED dies are integrated in a single packets. These LED packages may comprise, for example, a blue emitting LED die, a green emitting LED die and a red emitting LED die such that by providing a specific driving signal to each one of these LED dies, a multitude of emitted colors of light may be emitted by the Level 1 LED package. A gamut of such LED packages is relatively large. The LED packages with several LED dies that each emit another color may be used on, for example, flexible LED strips (in which a flexible strip acts as a printed circuit board) which are used for decorative lighting that may emit a controllable color of light.
By using blue emitting LED die, a green emitting LED die and a red emitting LED die one may generate colors of light within a relatively large portion of, for example, the CIE XYZ color space. However, the fact that about all colors of light may be generated by combining light emissions of blue emitting, a green emitting and a red emitting LED dies does not guarantee that the color rending of the emitted light is good. The blue emitting LED die, a green emitting LED die and a red emitting LED die emit light in a relatively narrow light emission spectrum which have, for example, a Full Width Half maximum value of 30 nanometers. When such narrow light emissions are combined, the light emission may have a color point close to the black body line in the CIE XYZ color space (and, thus appear white to the human naked eye), but the Color Rendering Index (CRI) of the emitted light will be relatively low. Thus, the Level 1 LED packages comprising blue emitting, a green emitting and a red emitting LED dies are not suitable for use as the main functional lighting, but are only suitable for decorative lighting purposes.
Published patent application US2009/0114932 discloses a light emitting diode light engine includes a substrate for supporting the LED light engine. The light emitting diode light engine comprises LEDs which include red LEDs, green LEDs and blue LEDs. Each of the blue LEDs is at least partially covered with a yellow phosphor coating compound. The concentration of the yellow phosphor coating compound is controlled to allow the emission of blue and yellow spectrum light energy from each blue LED. Emissions of light energy from the red LEDs, green LEDs and blue LEDs are combined to achieve a target correlated color temperature and a target color rendering index for the LED light engine.
The light emitting diode engine according to the above cited patent application is design to emit a color of light which is close to the black body line. This is done by using blue LEDs which are covered with a yellow phosphor such that relatively white light is generated. The green LEDs and red LEDs are used to control the color of the emitted light even better and, more in particular, to obtain a light emission that has a relatively high color rending index. The light emitting diode engine of the cited patent has the purpose to emit white light and does not have the purpose to emit a controllable color of light. At least is the gamut of the light emitting diode engine of the cited patent relatively small.
Document WO2008/026851A1 discloses a light emitting device comprising a first light emitting diode for emitting light in an ultraviolet wavelength region. At least one phosphor arranged around the first light emitting diode and excited by the light emitted from the first light emitting diode to emit light having a peak wavelength longer than the wavelength of the light emitted from the first light emitting diode. At least one second light emitting diode for emitting light having a wavelength different from the peak wavelength of the light emitted from the phosphor. According to this document, there is provided a white light emitting device, wherein using a light emitting diode for emitting light different in wavelength from light that is ex-cititively emitted from the phosphor, an excitation light source, i.e., light in the ultraviolet region for exciting the phosphor is effectively used, thereby improving energy conversion efficiency and improving reliability.
Document DE202011000007U1 discloses an arrangement for the generation of white light, comprising a support element, a first on the support element arranged LED for producing red light, a second on the support element arranged LED to produce blue and/or ultraviolet light, and a light-influencing element which is constructed and arranged such that at least part of the light of the second LED is converted into green light especially into a mint-green and/or greenish white light.
Document US2004/0217364A1 discloses a white light emitting lamp comprising a solid state ultra violet (UV) emitter that emits light in the UV wavelength spectrum. A conversion material is arranged to absorb at least some of the light emitting from the UV emitter and re-emit light at one or more different wavelengths of light. One or more complimentary solid state emitters are included that emit at different wavelengths of light than the UV emitter and the conversion material. The lamp emits a white light combination of light emitted from the complimentary emitters and from the conversion material. According to the disclosure, the white light having high efficacy and good color rendering. Other embodiments of white light emitting lamp according to the present invention comprises a solid state laser instead of a UV emitter. A high flux white emitting lamp embodiment comprises a large area light emitting diode that emits light at a first wavelength spectrum and includes a conversion material. A plurality of complimentary solid state emitters surround the large area LED, with each emitter emitting light in a spectrum different from the large area LED and conversion material such that the lamp emits a balanced white light. Scattering particles can be included in each of the embodiments to scatter the light from the emitters, conversion material and complimentary emitters to provide a more uniform emission.
Document US2011/0291114A1 discloses a light-emitting diode (LED) package structure that includes a substrate, a first LED, a second LED, and a resin material. At least one enclosure made of a transparent material is formed on a surface of the substrate, and encloses and forms at least one area on the substrate. The first LED and the second LED are disposed in the area and adjacent to each other, and the resin material is disposed in the area, and covers the first LED and the second LED. The LED package structure obtains desired illuminating lights by mixing lights respectively emitted by the first LED and the second LED.